Thank you :)
Hmm, yeah i made lots of thoughts about the airship theme and used the Bob-Omb theme from the minigames. But i'm planning to add some music-themes as an Add-On, where you can download additional music tracks for the mod :)

backgrounds are most likely not gonna happen, since the way they were done in this mod isn't possible in SMM 3DS afaik
Tilesets are easy and can be done in a day.
Enemies will just involve me not being so lazy

oh! no no, since the nsmbu backgrounds are not 3d models and instead 2d images in the 3ds version it's possible for it to be changed
EDIT: almost forgot! the nsmbu style's edit and create music should change too and no need to do the tilesets and edit/create music for the overworld since aboodxd already did it
EDIT 2: mabye if it's possible for you, you can change the editor pallet, style logo, and the theme lettering on the top left from 'New Super Mario Bros. U' to 'New Super Mario Bros. DS'